1. Field of the Invention
The present invention relates to a method of measuring dimension of a photo-mask pattern or a pattern on a wafer using a scanning electron microscope (SEM), and to a method of forming a photo-mask pattern or a pattern on a wafer.
2. Description of the Related Art
Recently, higher density integration advances in a semiconductor manufacturing process or in a thin-film manufacturing process for fabricating a thin-film element such as a thin-film magnetic head, and therefore a size of a photo-mask pattern or a wafer pattern formed on a wafer by the photo-mask becomes more narrower.
In the thin-film manufacturing process for fabricating the thin-film magnetic head, particularly, different size patterns with both a narrow size and a non-narrow or wide size are sometimes formed on a single photo-mask, and size differences between these patterns tend to increase. For example, poles of a magnetic write head element of the thin-film magnetic head have a pattern with a very small size and lapping sensors of the magnetic write head element such as write Resistance Lapping Guide (RLG) sensors have a pattern with a relatively larger size than that of the poles, and these patterns are formed on the single photo-mask.
According to the conventional measurement method, dimensions of these patterns with large differences in size could not be measured with the same accuracy. This is because, although such pattern dimensions will be in general measured by using a Critical Dimension (CD)-SEM, this CD-SEM can insure the measurement of pattern dimensions at the same accuracy only for patterns fallen within the same field of view at the same magnification of the SEM. For example, since the CD-SEM cannot measure a pattern with a dimension of 10 μm and a pattern with a dimension of 1 nm within the same field of view at the same magnification, it is impossible to obtain measured dimensions with the same accuracy. That is, when the size differences are too large, not only pattern dimensions cannot be accurately measured but also the measured accuracy cannot be checked. As a result, it is impossible to know whether the patterns are displaced or not.
Japanese patent publication No. 11-297588A discloses a method of measuring a displacement of a resist mask pattern formed on a wafer, not of a photo-mask. In the method, an optical measurement device measures a dimension of a large size pattern whereas a SEM measures a dimension of a small size pattern. However, according to this proposed method in which the large size pattern and the small size pattern are measured by different kinds of measurement device respectively, it is impossible to conform accuracies of both measured results to each other. Even in case that the large size pattern and the small size pattern are measured by the same measurement device, if the magnification differs in each measurement, measurement accuracies will never conform to each other.
Conventionally as aforementioned, since it was quite difficult to simultaneously and accurately measure dimensions of patterns with large differences, a designed dimension modified by a predicted error that was experimentally derived was used, in other words a pattern dimension was offset by an estimated value, instead of actual measurement of pattern dimension.